1. Field of the Invention
This invention relates to an electrical current sensor and, more particularly, to a transient response compensated current sensor that utilizes a Hall effect generator and non-inductive lead paths to eliminate any inductive loop area from exposure to the magnetic field produced by the electrical current being measured.
2. Description of the Background Art
Presently, many types of electrical current sensing sensors are known and are in wide use today throughout the electronics industry. Many of these sensors include a Hall effect generator that senses the magnetic field associated with an electrical current and, in turn, produces a Hall effect output voltage that is proportional to the magnetic field. However, many applications involve the measurement of an alternating or transient current. In these applications, errors in the Hall effect voltage will occur due to the changing magnetic field associated with the measured time varying current.
More particularly, the Hall effect output voltage is the voltage produced across opposite edges of an electrical current-carrying conductor when placed in a magnetic field. The basis of this effect, which depends upon the deflection of charged particles moving in a magnetic field, is the Lorentz force (F=Q(V.times.B)). This force is in a direction mutually perpendicular to the path of the particle movement and the magnetic field direction. As a result, an output voltage occurs across the Hall effect generator. This output voltage has a magnitude that depends upon the magnitude and angle of the impinging magnetic field, the Hall coefficient and the excitation current in the Hall effect generator. When the excitation current is held constant, the output voltage is proportional to the magnetic field produced by the current being sensed or measured.
Hall effect generators generally comprise a layer of homogeneous semiconductor material, known as the Hall plate, constructed upon a dielectric substrate. The excitation current is applied to the Hall plate through the use of contacts positioned on opposite ends of the Hall plate. When the Hall effect generator is placed in a magnetic field and supplied with excitation current, the Hall effect output voltage is produced in the Hall plate which is orthogonal to the magnetic field and the excitation current. In order to measure this Hall effect output voltage, output leads are attached to the Hall plate in a position opposite to each other and on the axis of the Hall effect output voltage. Thus, the output leads are also exposed to the magnetic field which is impinging upon the Hall effect generator.
As a result of the output leads being exposed to the magnetic field, unwanted voltages will be induced into the leads due to electromagnetic coupling occurring when the current being sensed is a time varying current. These induced voltages will add to the actual Hall effect output voltage formed in the Hall plate and cause errors in the measurement of the sensed current. As the magnitude and frequency of the time varying magnetic field increase, the induced voltages in the output leads will become larger and larger with respect to the actual Hall effect output voltage that is produced in the Hall plate.
Various types of sensing devices utilizing the Hall effect phenomena have been used in the past with an attempt to eliminate the error causing induced voltages in the output leads of the Hall generator. One example of a method for compensating for the induced voltages is seen in U.S. Pat. No. 3,551,706 (commonly assigned with this application), the disclosure of which is hereby incorporated by reference herein. In this patent, a pickup loop is mounted on the dielectric substrate of the Hall effect generator in an area aligned with the normal sensitivity area of the Hall plate also constructed on the substrate. The pickup loop is positioned in close proximity to the Hall plate to sense the same flux as that which impinges upon the Hall plate. The pickup loop is connected to the Hall effect output leads and is made much larger than any other loops formed by the output leads. The output leads including the pickup loop are then connected to a circuit which has a frequency response that complements the response produced by the interaction of the responses of the Hall plate, the pickup loop and the output leads to the impinging flux, thereby providing a resultant output response from the circuit that is flat within wide frequency ranges up to 4 MHz.
The Hall effect sensor disclosed in U.S. Pat. No. 3,551,706 achieved substantial commercial success. However, the difficulty in both manufacture and tuning the circuit during test compromised the economics of the sensor.
Another example of a method for compensating for the induced voltages is seen in U.S. Pat. No. 5,416,407 (commonly assigned with this application), the disclosure of which is hereby incorporated by reference herein. In this patent, an inductive loop is positioned on a PCB board at edge of the gap of a toroid core such that the inductive loop is exposed to the same impinging magnetic field as the Hall plate. The inductive loop is then connected in series opposition to the output leads of the Hall generator such that the induced voltages from the inductive loop are canceled out with the induced voltages from the output leads of the Hall generator.
This alternative has proven to be commercially acceptable as well, however, the additional inductive loop incorporated therein also acts as an antenna to external fields and does not completely cancel the original unwanted signal due to limiting manufacturing tolerances.
Therefore, it is an object of this invention to provide an improvement which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the Hall effect electrical current sensing art.
Another object of this invention is to provide a current sensor having an improved transient response, thereby resulting in more accurate measurements of sensed time varying currents.
Another object of this invention is to provide a current sensor that employs a flip chip packaged Hall effect generator that is electrically coupled to conductor traces that are figured to have a zero loop area perpendicular to the impinging magnetic field, thereby eliminating any unwanted induced voltages.
Another object of this invention is to provide a current sensor employing a Hall effect generator that is cost effective and provides repeatability from unit to unit.
Another object of this invention is to provide a sensor for sensing electrical current in a current carrying conductor comprising in combination: a printed circuit board formed from a dielectric material, said printed circuit board having a first surface and a second surface; a toroid core having a gap, the toroid core being coupled to the printed circuit board so as to facilitate receiving the current carrying conductor through the toroid core; a Hall effect generator, the Hall effect generator being surface mounted to the printed circuit board and located within the gap of the toroid core, the Hall effect generator being free of inductive leads; current source means for providing a control current, the current source means being electrically coupled to the Hall effect generator; amplifier means for amplifying the output voltage from the Hall effect generator; non-inductive circuit means for electrically coupling the amplifier means to the Hall effect generator free from any unwanted induced voltages being generated therein by the magnetic field; whereby a magnetic field is created in the toroid core and across the gap and across the Hall effect generator when electrical current flows through the current carrying conductor, the Hall effect generator producing an output voltage that is proportional to the magnetic field, the Hall effect generator and the non-inductive circuit means facilitating the prevention of unwanted voltages being introduced into the output voltage thereby achieving an improved transient response.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a more comprehensive understanding of the invention may be obtained by referring to the summary of the invention, and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.